In the last 10 years, while Microsoft has published all kinds of awesome games on the Xbox 360 (and has lately been quietly publishing XBLA games on the PC), it's published exactly three of its major shooters. Halo, Halo 2 and the first Gears of War.
It's a stupid move, one that seems increasingly stupid as time goes on (and the PC market grows ever stronger), but if you were hoping the madness would come ot a stop with Halo 4, sorry. It's not.
Microsoft has told Penny Arcade that "Halo 4 was designed specifically for Xbox 360, and while we're always exploring new ways to expand the franchise and share the Halo experience with as many fans as possible, we do not currently have any plans to port Halo 4 to PC".
Halo 4 isn't coming to the PC, and that's a mistake [Penny Arcade]